Lessons Flashcards
What is the X factor inactivation mechanism?
X-inactivation is the way which evolution chose to express the same amount of transcripts between males and females. Given that males have only one X chromosome, to reach an equilibrium females inactivate one of their two X chromosomes. By the third day of embryogenesis, one of the two X chromosomes in each cell starts becoming highly condensed into a type of heterochromatin. It’s called a Barr body and is located near the nuclear membrane.
Deletion mutation?
Most severe, might be complete or partial loss of function.
Duplication mutation?
It’s a structural abnormality involving the duplication of a specific sequence of the chromosome. It might result in a gain-of-function mutation, including oncogenic switches if the duplicated gene is a proto-oncogene; this is due to overexpression of duplicated genes.
Translocation mutation?
It’s the transfer of chromosomal material from a chromosome to another, and it’s caused by non-homologous recombination.It can be either balanced, with the maintenance of the total amount of genetic material, or unbalanced.
What is polyploidy?
variation in the number of haploid sets of chromosomes in an organism (ex. In humans, 23 x 3 = 69 chromosomes, three for each “number”, represents a triploidy). Variations can be caused by nondisjunction during meiosis. Only the standard diploidy is compatible with life in humans, save for some extreme and scarcely documented cases.
What is aneuploidy?
variation in the number of chromosomes to a quantity that is no longer a multiple of the haploid set (in humans, a multiple of 23).Examples of aneuploidies are trisomies.
Type 1 dynamic mutation?
is the expansion of a sequence in an exon, which causes a dominant gain-of-function mutation.
Examples of diseases caused by a type-1 dynamic mutation are Huntington Disease or Kennedy
Disease.
Type 1 dynamic mutation?
is the expansion of a sequence in an exon, which causes a dominant gain-of-function mutation. Examples of diseases caused by a type-1 dynamic mutation are Huntington Disease or Kennedy disease.
Type 2 dynamic mutation?
is the expansion of a sequence in a noncoding sequence which can either be 5’ UTR , 3’ UTR or an intron. Type-2 dynamic mutations are loss-of-function mutations.
Huntington’s disease?
Type 1 dynamic mutation caused by expansion of CAG triplet in the huntingtin gene. Dominant and neurodegenerative disease. Wild type is up to 39 repeats. Over 41 is pathogenic.
Fragile x syndrome?
Second most common cause of mental retardation in males. Expansion in the CGG sequence in the 5’ UTR of the FMR1 gene on X chromosome. Dominant. Repetition in wild type of up to 55 over 200 is pathogenic.
What is imprinting?
Imprinting is the epigenetic phenomenon behind expression differences between paternal and maternal chromosome regions. It is but a small collection of genes (100-150) inactivated or activated by methylation of CpG islands, depending on the derivation from either one of the parents.
Difference between mitochondrial and imprinted inheritance?
If, and only if, the mutation is in the mitochondrial genome, then mitochondrial inheritance is purely matrilineal. On the other hand, imprinted mutations can be passed on by both sexes, even in the case in which a mutation passed on by the parent for whom the gene is imprinted does not manifest the phenotype.
Mitochondrial DNA?
10 copies of its DNA, circular double stranded made of 37 genes. The external strand is heavy and the internal is light. The genes in code for 13 proteins, 22 tRNAs and 2 rRNAs.
Mendelian mitochondrial inheritance and proper mitochondrial inheritance?
Mendelian one, which is cause by a mutation in mitochondrial genes found the nuclear genome.
A “proper” mitochondrial one, which is matrilineal only (paternal mitochondria are lost when the sperms fertilizes the oocyte).
What is epigenetics?
Epigenetics is the study of mitotically/meiotically inherited modifications of gene function that aren’t caused by modifications of the sequence.
What is DNA methylation and what does it do?
DMT1 (DNA-binding methyl transferase 1) transfers methyl groups on the cytosines, converting them into 5’-methyl cytosines. Methylation of a DNA region usually means the blocking of transcription of that region, both because methylated DNA hinders TFs attachment and because methyl-binding proteins help keeping the region untranscribed.
What are karyotypes?
It’s the number and appearance of chromosomes in the nucleus of a eukaryotic cell. A karyotype can be obtained from metaphase cells in order to examine eventual chromosomal mutations, such as aneuploidies, or deletions or duplications of genes, using optic microscopy.
The two exams associated with this kind of analysis are F.I.S.H. and Array-CGH.
Karyotypes are usually obtained by white blood cells,
What is F.I.S.H and Array CGH?
FISH stands for “Fluorescent In Situ Hybridization”. It’s a mechanism that allows the location of specific sequences in a karyotype.
Array-CGH stands for “Array-Comparative Genomic Hybridization”.
It’s a technique through which two whole genomes can be compared in order to identify eventual chromosomal mutations.
What is epistasis?
Epistasis refers to cases in which the effect of one gene (or allele) masks or modifies the effect of another gene. In other words, it’s the case where gene (or allele) A controls the action of gene (or allele) B, or lies upstream of gene B in a pathway.
What is incomplete dominance?
Incomplete dominance is a phenomenon that causes a non-Mendelian pattern of inheritance. In fact, heterozygotes for an allele with incomplete dominance show a phenotype that will be intermediate between that of the homozygote dominant and that of the homozygote recessive
What is over-dominance?
Overdominance is a phenomenon that involves environmental factors which interact with specific genotypes to bring forth a selection of them for survival.
What is pleiotropy?
Pleiotropy is a phenomenon that underlies specific monogenic mutations: it influences a plurality of functions of the organism, therefore causing a multisystemic disease. Ex cystic fibrosis and Marfan syndrome.
